Organic electroluminescent materials and devices

ABSTRACT

An OLED is disclosed whose emissive layer has a first host and an emitter, where the emitter is a phosphorescent metal complex or a delayed fluorescent emitter, where EHIT, the T1 triplet energy of the first host, is higher than EET, the T1 triplet energy of the emitter, where EET is at least 2.50 eV, where the LUMO energy of the first host is higher than the HOMO energy of the emitter, where the absolute value of the difference between the HOMO energy of the emitter and the LUMO energy of the first host is ΔE1, where a≤ΔE1−EET≤b; and where a≥0.05 eV, and b≤0.60 eV.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority toU.S. Provisional Application Ser. No. 62/537,029, filed Jul. 26, 2017,the entire contents of which is incorporated herein by reference.

FIELD

The present invention relates to a novel device structure for an organiclight emitting device that emits light in blue spectrum region with anelectron transporting host and/or hole transporting host having specificenergy levels.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs.The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative) Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

There continues to be a great challenge in the OLED industry to achievecommercial high performance blue light emitting devices, i.e., devicesemitting blue color (maximum wavelengths of the emission spectra lessthan about 500 nm) (hereinafter “blue device”), with high efficiency andlonger device lifetime. In the past, blue light emitting devices mainlyused either a wide bandgap host material or a hole-transporting hostmaterial in the emissive layer. In this disclosure, inventors disclosenovel devices that utilize an electron-transporting host (e-host)material and/or a hole-transporting host (h-host) material with specificenergy requirements. These new devices can significantly improve overalldevice performance.

An OLED is disclosed wherein the OLED comprises an anode, a cathode, andan organic emissive layer disposed between the anode and the cathode.The organic emissive layer comprises a first host and an emitter. Thefirst host and the emitter each being of a material having a HOMOenergy, a LUMO energy, and a T₁ triplet energy. The emitter is selectedfrom the group consisting of a phosphorescent metal complex, and adelayed fluorescent emitter. E_(HIT), the T₁ triplet energy of the firsthost, is higher than E_(ET), the T₁ triplet energy of the emitter,wherein E_(ET) is at least 2.50 eV. The LUMO energy level of the firsthost is higher than the HOMO energy level of the emitter. The absolutevalue of the difference between the HOMO of the emitter and the LUMO ofthe first host is represented by ΔE1, wherein a≤ΔE1−E_(ET)≤b, wherea≥0.005 eV, and b≤0.60 eV.

In some embodiments, an OLED is disclosed wherein the OLED comprises ananode, a cathode, and an organic emissive layer disposed between theanode and the cathode. The organic emissive layer comprises a firsthost, a second host, and an emitter. The first host, the second host,and the emitter each being of a material having a HOMO energy, a LUMOenergy, and a T₁ triplet energy. The emitter is selected from the groupconsisting of a phosphorescent metal complex, and a delayed fluorescentemitter. E_(HIT), the T₁ triplet energy of the first host, is higherthan E_(ET), the T₁ triplet energy of the emitter, wherein E_(ET) is atleast 2.50 eV. The HOMO energy level of the first host is higher thanthe HOMO energy level of the second host, and the absolute value of thedifference between the HOMO of the emitter and the HOMO of the firsthost is represented by ΔE2, wherein ΔE2≤d, wherein d is 1.2 eV. Theabsolute value of the difference between the LUMO of the emitter and theHOMO of the first host is represented by ΔE3, wherein a≤ΔE3−E_(ET)≤b,wherein a≥0.05 eV, and b≤0.60 eV.

In some embodiments, an OLED is disclosed wherein the OLED comprises ananode, a cathode, and an organic emissive layer disposed between theanode and the cathode. The organic emissive layer comprises a first hosthaving a HOMO energy, a LUMO energy, and a T₁ triplet energy; a secondhost having a HOMO energy, a LUMO energy, and a T₁ triplet energy; athird host having a HOMO energy, a LUMO energy, and a T₁ triplet energy;and an emitter having a HOMO energy, a LUMO energy, and a T₁ tripletenergy. The emitter is a phosphorescent metal complex having E_(ET), T₁triplet energy, of at least 2.50 eV. The LUMO energy of the first hostis higher than the HOMO energy of the emitter, where the absolute valueof the difference between the HOMO energy of the emitter and the LUMOenergy of the first host is ΔE1. The HOMO energy of the second host islower than the HOMO energy of the emitter, where the absolute value ofthe difference between the HOMO energy of the emitter and the HOMOenergy of the second host is ΔE4. In this embodiment, a≤ΔE1−E_(ET)≤b,wherein a≥0.005 eV and b≤0.60 eV; where ΔE4≤d, wherein d is 1.2 eV; andwhere the HOMO energy of the third host is lower than the HOMO energy ofthe second host

In some embodiments, an OLED is disclosed wherein the OLED comprises ananode, a cathode, and an organic emissive layer disposed between theanode and the cathode. The organic emissive layer comprises a first hosthaving a HOMO energy, a LUMO energy, and a T₁ triplet engery; a secondhost having a HOMO energy, a LUMO energy, and a T₁ triplet engery; and athird host having a HOMO energy, a LUMO energy, and a T₁ triplet engery;and an emitter having a HOMO energy, a LUMO energy, and a T₁ tripletengery. The emitter is a phosphorescent metal complex having E_(ET), theT₁ triplet energy, of at least 2.50 eV. The LUMO energy of the firsthost is highter than the HOMO energy of the emitter. The absolute valueof the difference between the HOMO energy level of the second host andthe LUMO energy of the first host is ΔE5. The HOMO energy of the secondhost is higher than the HOMO energy of the emitter, where the absolutevalue of the difference between the HOMO energy level of the emitter andthe HOMO energy of the second host is ΔE4. In this embodiment,a≤ΔE5−E_(ET)≤b, where a≥0.005 eV, and b≤0.60 eV, and where ΔE4≤d; andwherein d is 1.2 eV.

According to yet another embodiment, a consumer product comprising oneor more of the OLEDs disclosed herein is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 illustrates the relative HOMO and LUMO energy levels of the firstemitter and the first host in a one host, one emitter system deviceaccording to some embodiments.

FIG. 4 illustrates the relative HOMO and LUMO energy levels of the firstemitter, the first host, and the second host in a one emitter, two hostssystem device according to some embodiments.

FIG. 5 illustrates the relative HOMO and LUMO energy levels of the firstemitter, the first host, and the second host in a one emitter, two hostssystem device according to some embodiments.

FIG. 6A shows the relative HOMO and LUMO energy levels of the firstemitter, the first host, and the second host in a one emitter, two hostssystem device according to some embodiments. The HOMO of the first hostis deeper than the HOMO of the first emitter by ΔE₂.

FIG. 6B shows the relative HOMO and LUMO energy levels of the firstemitter, the first host, and the second host in a one emitter, two hostssystem device according to some embodiments. The HOMO level of the firsthost shallower than the HOMO level of the first emitter by ΔE₂.

FIG. 7 shows the relative HOMO and LUMO energy levels of the firstemitter, the first host, the second host, and the third host in a oneemitter, three hosts system device according to some embodiments.

FIG. 8 shows the relative HOMO and LUMO energy levels of the firstemitter the first host, the second host, and the third host in a oneemitter, three hosts system device according to some other embodiments.

FIG. 9 shows a plot of photoluminescence of Emitter 2 in drop cast poly(methyl methacrylate) (PMMA) at room temperature demonstrating theintrinsic emission spectrum of Emitter 2.

FIG. 10 is a schematic illustration of a red probe device 300 with thematerials for the layers other than the emissive layer (EML) specified.The dashed lines indicate the different locations where the red sensinglayer was inserted. The locations for the red sensing layer is markedwith distances relative to the EBL/EML interface 332 and are reported inangstroms.

FIG. 11A shows the electroluminescent spectra from three example redprobe devices each with a red sensing layer formed of 20Å thick Compound9 provided at a distance of 0 Å, 150 Å, and 300 Å from the EBL ofCompound 4.

FIG. 11B shows the normalized red to blue intensity ratio (R/B) as afunction of the position of the sensing layer. The higher the R/B valuethe larger the exciton population at that spatial location. Themeasurements were taken at driving current density of 10 mA/cm².

FIG. 12 whos the R/B ratio of the device from FIGS. 11A and 11B atdriving densities of 1, 10, and 100 mA/cm². Thus, the plot for the R/Bratio taken at 10 mA/cm² is the same plot shown in FIG. 11B.

FIGS. 13A-13C are plots of R/B ratio as a function of driving currentdensity for Device 2 a, Device 2 b, Device 2 c, and Device 2 d,respectively.

FIG. 14 illustrates the relative HOMO and LUMO energy levels of thefirst emitter, the first host, the second host, and the third host in athree hosts system device according to some embodiments.

FIG. 15 shows the electroluminescent spectra of the experimental devicesDevice 1 and Device 2.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. 7,279,704 at cols. 6-10, which are incorporated byreference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and organic vaporjet printing (OVJP). Other methods may also be used. The materials to bedeposited may be modified to make them compatible with a particulardeposition method. For example, substituents such as alkyl and arylgroups, branched or unbranched, and preferably containing at least 3carbons, may be used in small molecules to enhance their ability toundergo solution processing. Substituents having 20 carbons or more maybe used, and 3-20 carbons is a preferred range. Materials withasymmetric structures may have better solution processibility than thosehaving symmetric structures, because asymmetric materials may have alower tendency to recrystallize. Dendrimer substituents may be used toenhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. A consumer product comprising an OLED thatincludes the compound of the present disclosure in the organic layer inthe OLED is disclosed. Such consumer products would include any kind ofproducts that include one or more light source(s) and/or one or more ofsome type of visual displays. Some examples of such consumer productsinclude flat panel displays, curved displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, rollable displays, foldabledisplays, stretchable displays, laser printers, telephones, mobilephones, tablets, phablets, personal digital assistants (PDAs), wearabledevices, laptop computers, digital cameras, camcorders, viewfinders,micro-displays (displays that are less than 2 inches diagonal), 3-Ddisplays, virtual reality or augmented reality displays, vehicles, videowalls comprising multiple displays tiled together, theater or stadiumscreen, and a sign. Various control mechanisms may be used to controldevices fabricated in accordance with the present invention, includingpassive matrix and active matrix. Many of the devices are intended foruse in a temperature range comfortable to humans, such as 18 degrees C.to 30 degrees C., and more preferably at room temperature (20-25 degreesC.), but could be used outside this temperature range, for example, from−40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms “halo,” “halogen,” and “halide” are used interchangeably andrefer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_(s)).

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—R_(s) or—C(O)—O—R_(s)) radical.

The term “ether” refers to an —OR_(s) radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and referto a —SR_(s) radical.

The term “sulfinyl” refers to a —S(O)—R_(s) radical.

The term “sulfonyl” refers to a —SO₂—R_(s) radical.

The term “phosphino” refers to a —P(R_(s))₃ radical, wherein each R_(s)can be same or different.

The term “silyl” refers to a —Si(R_(s))₃ radical, wherein each R can besame or different.

In each of the above, R_(s) can be hydrogen or a substituent selectedfrom the group consisting of deuterium, halogen, alkyl, cycloalkyl,heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl,alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, andcombination thereof. Preferred R_(s) is selected from the groupconsisting of alkyl, cycloalkyl, aryl, heteroaryl, and combinationthereof

The term “alkyl” refers to and includes both straight and branched chainalkyl radicals. Preferred alkyl groups are those containing from one tofifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl,butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl,2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl,and the like. Additionally, the alkyl group isoptionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, andspino alkyl radicals. Preferred cycloalkyl groups are those containing 3to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl,cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl,adamantyl, and the like. Additionally, the cycloalkyl group may beoptionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or acycloalkyl radical, respectively, having at least one carbon atomreplaced by a heteroatom. Optionally the at least one heteroatom isselected from O, S, N, P, B, Si and Se, preferably, O, S or N.Additionally, the heteroalkyl or heterocycloalkyl group is optionallysubstituted.

The term “alkenyl” refers to and includes both straight and branchedchain alkene radicals. Alkenyl groups are essentially alkyl groups thatinclude at least one carbon-carbon double bond in the alkyl chain.Cycloalkenyl groups are essentially cycloalkyl groups that include atleast one carbon-carbon double bond in the cycloalkyl ring. The term“heteroalkenyl” as used herein refers to an alkenyl radical having atleast one carbon atom replaced by a heteroatom. Optionally the at leastone heteroatom is selected from O, S, N, P, B, Si, and Se, preferably,O, S, or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups arethose containing two to fifteen carbon atoms. Additionally, the alkenyl,cycloalkenyl, or heteroalkenyl group is optionally substituted.

The term “alkynyl” refers to and includes both straight and branchedchain alkyne radicals. Preferred alkynyl groups are those containing twoto fifteen carbon atoms. Additionally, the alkynyl group is optionallysubstituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer toan alkyl group that is substituted with an aryl group. Additionally, thearalkyl group is optionally substituted.

The term “heterocyclic group” refers to and includes aromatic andnon-aromatic cyclic radicals containing at least one heteroatom.Optionally the at least one heteroatom is selected from O, S, N, P, B,Si, and Se, preferably, O, S, or N. Hetero-aromatic cyclic radicals maybe used interchangeably with heteroaryl. Preferred hetero-non-aromaticcyclic groups are those containing 3 to 7 ring atoms which includes atleast one hetero atom, and includes cyclic amines such as morpholino,piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers,such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and thelike. Additionally, the heterocyclic group may be optionallysubstituted.

The term “aryl” refers to and includes both single-ring aromatichydrocarbyl groups and polycyclic aromatic ring systems. The polycyclicrings may have two or more rings in which two carbons are common to twoadjoining rings (the rings are “fused”) wherein at least one of therings is an aromatic hydrocarbyl group, e.g., the other rings can becycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls.Preferred aryl groups are those containing six to thirty carbon atoms,preferably six to twenty carbon atoms, more preferably six to twelvecarbon atoms. Especially preferred is an aryl group having six carbons,ten carbons or twelve carbons. Suitable aryl groups include phenyl,biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene,anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene,perylene, and azulene, preferably phenyl, biphenyl, triphenyl,triphenylene, fluorene, and naphthalene. Additionally, the aryl groupmay be optionally substituted.

The term “heteroaryl” refers to and includes both single-ringhetero-aromatic groups and polycyclic aromatic ring systems that includeat least one heteroatom. The heteroatoms include, but are not limited toO, S, N, P, B, Si, and Se. In many instances, O, S, or N are thepreferred heteroatoms. Hetero-single ring aromatic systems arepreferably single rings with 5 or 6 ring atoms, and the ring can havefrom one to six heteroatoms. The hetero-polycyclic ring systems can havetwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles, and/or heteroaryls. The hetero-polycyclic aromaticring systems can have from one to six heteroatoms per ring of thepolycyclic aromatic ring system. Preferred heteroaryl groups are thosecontaining three to thirty carbon atoms, preferably three to twentycarbon atoms, more preferably three to twelve carbon atoms. Suitableheteroaryl groups include dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine, preferablydibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole,indolocarbazole, imidazole, pyridine, triazine, benzimidazole,1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogsthereof. Additionally, the heteroaryl group may be optionallysubstituted.

Of the aryl and heteroaryl groups listed above, the groups oftriphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran,dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine,pyrazine, pyrimidine, triazine, and benzimidazole, and the respectiveaza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl,and heteroaryl, as used herein, are independently unsubstituted orsubstituted with one or more general substituents.

In many instances, the general substituents are selected from the groupconsisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile,sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl,heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, andcombinations thereof

In some instances, the preferred general substituents are selected fromthe group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy,aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinationsthereof

In yet other instances, the more preferred general substituents areselected from the group consisting of deuterium, fluorine, alkyl,cycloalkyl, aryl, heteroaryl, and combinations thereof

The term “substituted” refers to a substituent other than H that isbonded to the relevant position, e.g., a carbon. For example, where R¹represents mono-substituted, then one R¹ must be other than H.Similarly, where R¹ represents di-substituted, then two of R¹ must beother than H. Similarly, where R¹ is unsubstituted, R¹ is hydrogen forall available positions. The maximum number of substitutions possible ina structure (for example, a particular ring or fused ring system) willdepend on the number of atoms with available valencies.

As used herein, “combinations thereof” indicates that one or moremembers of the applicable list are combined to form a known orchemically stable arrangement that one of ordinary skill in the art canenvision from the applicable list. For example, an alkyl and deuteriumcan be combined to form a partial or fully deuterated alkyl group; ahalogen and alkyl can be combined to form a halogenated alkylsubstituent; and a halogen, alkyl, and aryl can be combined to form ahalogenated arylalkyl. In one instance, the term substitution includes acombination of two to four of the listed groups. In another instance,the term substitution includes a combination of two to three groups. Inyet another instance, the term substitution includes a combination oftwo groups. Preferred combinations of substituent groups are those thatcontain up to fifty atoms that are not hydrogen or deuterium, or thosewhich include up to forty atoms that are not hydrogen or deuterium, orthose that include up to thirty atoms that are not hydrogen ordeuterium. In many instances, a preferred combination of substituentgroups will include up to twenty atoms that are not hydrogen ordeuterium.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo [f,h]quinoxaline and dibenzo[fh]quinoline. Oneof ordinary skill in the art can readily envision other nitrogen analogsof the aza-derivatives described above, and all such analogs areintended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuteratedcompounds can be readily prepared using methods known in the art. Forexample, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, andU.S. Pat. Application Pub. No. US 2011/0037057, which are herebyincorporated by reference in their entireties, describe the making ofdeuterium-substituted organometallic complexes. Further reference ismade to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt etal., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which areincorporated by reference in their entireties, describe the deuterationof the methylene hydrogens in benzyl amines and efficient pathways toreplace aromatic ring hydrogens with deuterium, respectively.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. phenyl, phenylene,naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g.benzene, naphthalene, dibenzofuran). As used herein, these differentways of designating a substituent or attached fragment are considered tobe equivalent.

An OLED is disclosed wherein the OLED comprises an anode, a cathode, andan organic emissive layer disposed between the anode and the cathode.The organic emissive layer comprises a first host and an emitter,wherein the emitter is selected from the group consisting of aphosphorescent metal complex, and a delayed fluorescent emitter.E_(HIT), the T₁ triplet energy of the first host, is higher than E_(ET),the T₁ triplet energy of the emitter, wherein E_(ET) is at least 2.50eV. The LUMO energy level of the first host is higher than the HOMOenergy level of the emitter. The absolute value of the differencebetween the HOMO of the emitter and the LUMO of the first host isrepresented by ΔE1 and wherein a≤ΔE1−E_(ET)≤b, where a≥0.05 eV, andb≤0.60 eV. This energy configuration is illustrated in FIG. 3.

In some embodiments, the relationship a≤ΔE1−E_(ET)≤b is maintained wherea is 0.10 eV. In some embodiments a is 0.15 eV. In some embodiments, ais 0.20 eV. In some embodiments, b is 0.50 eV. In some embodiments, b is0.40 eV. In some embodiments, b is 0.30 eV. In some embodiments, b is0.25 eV. In some embodiments, E_(ET) is at least 2.60 eV. In someembodiments, E_(ET) is at least 2.70 eV. In some embodiments, E_(ET) isat least 2.75 eV. In some embodiments, E_(ET) is at least 2.80 eV.

In some embodiments of the OLED, the emitter is a phosphorescent metalcomplex. In some embodiments of the OLED, the emitter is a delayedfluorescent emitter.

In some embodiments of the OLED, the first host is an e-host.

In some embodiments of the OLED, the absolute value of the differencebetween the highest HOMO energy and the lowest LUMO energy among allcomponents in the emissive layer is larger than E_(ET) by at least a.

Referring to FIGS. 4 and 5, in some embodiments of the OLED, the OLEDfurther comprises a second host and E_(H2T), T₁ triplet energy of thesecond host, is higher than E_(ET). As illustrated in FIG. 4, in someembodiments, the HOMO energy of the second host is lower than the HOMOenergy of the first host, and the LUMO energy of the second host ishigher than the LUMO energy of the first host. As illustrated in FIG. 5,in some embodiments, the HOMO energy of the second host is higher thanthe HOMO energy of the first host, and the LUMO energy of the secondhost is higher than the LUMO energy of the first host.

In some embodiments, the difference between the HOMO energy levels ofthe first host and the second host is from 0.1 to 0.6 eV. As disclosedherein, when energy levels are referred to as being from aa to bb eV, itincludes the end values aa and bb. In some embodiments, the differencebetween the HOMO energy levels between the first host and the secondhost is from 0.1 to 0.3 eV. In some embodiments, the difference betweenthe HOMO energy levels between the first host and the second host isfrom 0.1 to 0.2 eV. In some embodiments, the difference between the HOMOenergy levels between the first host and the second host is from 0.1 to0.15 eV. In some embodiments, the difference between the LUMO energylevels between the first host and the second host is from 0.1 to 0.50eV. In some embodiments, the difference between the LUMO energy levelsbetween the first host and the second host is from 0.1 to 0.35 eV. Insome embodiments, the difference between the LUMO energy levels betweenthe first and the second host is from 0.1 to 0.20 eV. In someembodiments, the first host, the second host, and the emitter are theonly components in the emissive layer.

In some embodiments, the second host is a hole transporting host.

In some embodiments of the OLED, the OLED has an operating voltage ofless than 6.0 Vat 10 mA/cm². In some embodiments, the OLED has anoperating voltage of less than 5.0 Vat 10 mA/cm². In some embodiments,the OLED has an operating voltage of less than 4.0 V at 10 mA/cm².

In some embodiments of the OLED, the first host comprises at least onechemical group selected from the group consisting of pyridine,pyrimidine, pyrazine, triazine, imidazole, aza-tripheny lene,aza-carbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene.

In some embodiments of the OLED, the emitter is a phosphorescent blueemitter.

In some embodiments of the OLED, the emitter has the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z); where L¹, L² and L³ can be the same ordifferent; where x is 1, 2, or 3; where y is 0, 1, or 2; where z is 0,1, or 2; where x+y+z is the oxidation state of the metal M; where L¹, L²and L³ are each independently selected from the group consisting of:

where each X¹ to X¹⁷ are independently selected from the groupconsisting of carbon and nitrogen; where Xis selected from the groupconsisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″,GeR′R″; where R′ and R″ are optionally fused or joined to form a ring;where each R_(a), R_(b), R_(c), and R_(d) may represent from monosubstitution to the possible maximum number of substitution, or nosubstitution; where R′, R″, R_(a), R_(b), R_(c), and R_(d) are eachindependently selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof; and wherein any two R_(a), R_(b),R_(c), and R_(d) are optionally fused or joined to form a ring or form amultidentate ligand.

In some embodiments of the OLED where the emitter has the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), R′, R″, R_(a), R_(b), R_(c), and R_(d) areeach independently selected from the group consisting of hydrogen,deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl,nitrile, isonitrile, sulfanyl, and combinations thereof.

In some embodiments of the OLED where the emitter has the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula selected fromthe group consisting of Ir(L¹)(L²)(L³), Ir(L¹)₂(L²), and Ir(L¹)₃;wherein L¹, L² and L³ are different and each independently selected fromthe group consisting of:

In some embodiments of the OLED where the emitter has the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of Pt(L¹)₂ orPt(L¹)(L²). In some embodiments, L¹ is connected to the other L¹ or L²to form a tetradentate ligand.

In some embodiments of the OLED where the emitter has the formula ofM(L¹)_(x)(L²)_(y)(L³)_(z), the compound has the formula of M(L¹)₂ orM(L¹)(L²); wherein M is Ir, Rh, Re, Ru, or Os, L¹ and L² are each adifferent tridentate ligand. In some embodiments, L¹, is selected fromthe group consisting of:

A consumer product comprising an OLED is also disclosed. The OLEDcomprises an anode, a cathode, and an organic emissive layer disposedbetween the anode and the cathode. The organic emissive layer comprisesa first host and an emitter, wherein the emitter is selected from thegroup consisting of a phosphorescent metal complex, and a delayedfluorescent emitter. E_(HIT), the T₁ triplet energy of the first host,is higher than E_(ET), the T₁ triplet energy of the emitter, whereinE_(ET) is at least 2.50 eV. The LUMO energy of the first host is higherthan the HOMO energy of the emitter. The absolute value of thedifference between the HOMO energy of the emitter and the LUMO energy ofthe first host is represented by ΔE1 and wherein a≤ΔE1−E_(ET)≤b, wherea≥0.05 eV, and b≤0.60 eV.

An OLED according to another embodiment is disclosed, comprising: ananode; a cathode; and an organic emissive layer disposed between theanode and the cathode, the organic emissive layer comprising: a firsthost, a second host; and an emitter; wherein the emitter is selectedfrom the group consisting of a phosphorescent metal complex, and adelayed fluorescent emitter; wherein E_(HIT), the T₁ triplet energy ofthe first host, is higher than E_(ET), the T₁ triplet energy of theemitter; wherein E_(ET) is at least 2.50 eV; wherein the HOMO energy ofthe first host is higher than the HOMO energy of the second host;wherein the absolute value of the difference between the HOMO energy ofthe emitter and the HOMO energy of the first host is ΔE2; wherein ΔE2≤d;wherein d is 1.2 eV; wherein the absolute value of the differencebetween the LUMO energy of the emitter and the HOMO energy of the firsthost is represented by ΔE3; wherein the following relationshipa≤ΔE3−E_(ET)≤b is maintained; wherein a≥0.05 eV, and b≥0.60 eV. Thisenergy configuration is shown in FIGS. 6A and 6B. In some embodiments ofthe OLED, d is 0.8 eV. In some embodiments, d is 0.5 eV. In someembodiments, a is 0.05 eV and b is 0.4 eV. In some embodiments, a is0.05 eV and b is 0.2 eV. In some embodiments, a is 0.10 eV, 0.15 eV, or0.20 eV. In some embodiments, b is 0.50 eV, 0.40 eV, 0.30 eV, or 0.25eV. In some embodiments, E_(ET) is at least 2.60 eV. In someembodiments, E_(ET) is at least 2.70 eV. In some embodiments, E_(ET) isat least 2.75 eV. In some embodiments, E_(ET) is at least 2.80 eV.

An OLED according to another embodiment is disclosed that comprises: ananode; a cathode; and an organic emissive layer disposed between theanode and the cathode. The organic emissive layer comprises: a firsthost, a second host, and a third host; and an emitter; wherein theemitter is a phosphorescent metal complex having E_(ET), T₁ tripletenergy, of at least 2.50 eV; wherein the absolute value of thedifference between the HOMO of the emitter and the LUMO of the firsthost is represented by ΔE1; wherein the absolute value of the differencebetween the HOMO of the emitter and the HOMO of the second host is ΔE4;wherein the following relationship a≤ΔE1−E_(ET)≤b is maintained whereina≥0.005 eV, and b≤0.60 eV; wherein ΔE4≤d; wherein d is 1.2 eV; andwherein the absolute energy difference between the HOMO level of thethird host and the first emitter is greater than ΔE4. This energyconfiguration is shown in FIG. 7. In some embodiments of the OLED, d is0.8 eV. In some embodiments, d is 0.5 eV. In some embodiments, a is0.005 eV and b is 0.4 eV. In some embodiments, a is 0.005 eV and b is0.2 eV. In some embodiments, a is 0.10 eV, 0.15 eV, or 0.20 eV. In someembodiments, b is 0.50 eV, 40 eV, 0.30 eV, or 0.25 eV. In someembodiments, E_(ET) is at least 2.60 eV. In some embodiments, E_(ET) isat least 2.70 eV. In some embodiments, E_(ET) is at least 2.75 eV. Insome embodiments, E_(ET) is at least 2.80 eV.

In some embodiments, an OLED is disclosed that comprises: an anode; acathode; and an organic emissive layer disposed between the anode andthe cathode. The organic emissive layer comprises: a first host, asecond host, and a third host; and an emitter; wherein the emitter is aphosphorescent metal complex having E_(ET), T₁ triplet energy, of atleast 2.50 eV; wherein the absolute value of the difference between theHOMO of the second host and the LUMO of the first host is represented byDES; wherein the absolute value of the difference between the HOMO ofthe emitter and the HOMO of the second host is ΔE4; wherein thefollowing relationship a≤ΔE5−E_(ET)≤b is maintained wherein a≥0.005 eV,and b≥0.60 eV; wherein ΔE4≤d; and wherein d is 1.2 eV. This energyconfiguration is shown in FIG. 14. In some embodiments of the OLED, d is0.6 eV. In some embodiments, d is 0.3 eV. In some embodiments, a is0.005 eV and b is 0.4 eV. In some embodiments, a is 0.005 eV and b is0.2 eV. In some embodiments, a is 0.10 eV, 0.15 eV, or 0.20 eV. In someembodiments, b is 0.50 eV, 0.40 eV, 0.30 eV, or 0.25 eV. In someembodiments, E_(ET) is at least 2.60 eV. In some embodiments, E_(ET) isat least 2.70 eV. In some embodiments, E_(ET) is at least 2.75 eV. Insome embodiments, E_(ET) is at least 2.80 eV.

The following are some examples of host materials that are suitable foruse as the first host, the second host, and the third host, depending onthe particular emitter compound that is selected.

The HOMO, LUMO, and E_(ET) of Compound 1, Compound 2, Compound 3,Compound 4, and Compound 10, are provided below in Table 1. Theoxidation of Compound 1 is outside the window of the solvent ofdimethylformamide. This means that the oxidation of Compound 1 is higherthan 1.13 V which corresponds to HOMO deeper than −5.93 eV.

TABLE 1 Material HOMO (eV) LUMO (eV) E_(ET) (eV) Compound 1 <−5.93 −2.712.86 Compound 2 −5.7 −2.47 2.95 Compound 3 −5.73 −2.12 2.95 Compound 4−5.38 −1.84 2.74 Compound 10 −5.68 −1.99 2.99

The following are some examples of emitter compounds that are suitablefor use with the example host compounds.

The HOMO, LUMO, and E_(ET) of Emitter 2, and Emitter 3 are providedbelow in Table 2.

TABLE 2 Material HOMO (eV) LUMO (eV) E_(ET) (eV) Emitter 2 −5.37 −2.182.76 Emitter 3 −5.40 −2.22 2.76

The following are some examples of charge transport materials and redsensing compounds.

The HOMO, LUMO, and E_(ET) levels for any given organic compounds can bereadily measured and one of ordinary skill in the art would know how tomeasure these energy values and select the appropriate combination ofemitter, first host, second host, and third host compounds that wouldmeet the energy configurations disclosed hereion. For example, tomeasure the energy levels, the inventors performed solution cyclicvoltammetry (CV) and differential pulsed voltammetry using a CHInstruments model 6201B potentiostat using anhydrous dimethylformamidesolvent and tetrabutylammonium hexafluorophosphate as the supportingelectrolyte. Glassy carbon, and platinum and silver wires were used asthe working, counter and reference electrodes, respectively.Electrochemical potentials were referenced to an internalferrocene-ferroconium redox couple (Fc/Fc+) by measuring the peakpotential differences from differential pulsed voltammetry. Thecorresponding HOMO and LUMO energies were determined by referencing thecationic and anionic redox potentials to ferrocene (4.8 eV vs. vacuum)according to literature. The T₁ triplet energy of the materials ismeasured by dissolving the material in 2-methyl tetrahydrofuran andcooling the mixture to 77K to form a frozen glass. The photoluminescenceis measured using a Horiba Fluorolog florimeter and the T₁ is taken as1^(st) emission peak. When the HOMO and LUMO are measured in the solidstate with techniques such as Ultraviolet Photoelectron Spectroscopy(UPS) or Inverse Photolectron Spectroscopy (IPES) the actual values aregenerally different than those measured with CV method. However, therelative difference in the energy levels between different molecues isfairly similar regardless of the measurement technique used. Thus, solong as one compares the relative energy level difference using the sametechnique, the energy difference should be similar for a given set ofmolecules being compared.

In some embodiments, the OLED has one or more characteristics selectedfrom the group consisting of being flexible, being rollable, beingfoldable, being stretchable, and being curved. In some embodiments, theOLED is transparent or semi-transparent. In some embodiments, the OLEDfurther comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising adelayed fluorescent emitter. In some embodiments, the OLED comprises aRGB pixel arrangement or white plus color filter pixel arrangement. Insome embodiments, the OLED is a mobile device, a hand held device, or awearable device. In some embodiments, the OLED is a display panel havingless than 10 inch diagonal or 50 square inch area. In some embodiments,the OLED is a display panel having at least 10 inch diagonal or 50square inch area. In some embodiments, the OLED is a lighting panel.

An emissive region in an OLED is disclosed. The emissive regioncomprising a first host and an emitter, wherein the emitter is selectedfrom the group consisting of a phosphorescent metal complex, and adelayed fluorescent emitter. The T₁ triplet energy of the first hostE_(HIT) is higher than the T₁ triplet energy of the emitter E_(ET),wherein E_(ET) is at least 2.50 eV. The LUMO energy of the first host ishigher than the HOMO energy of the emitter. The absolute value of thedifference between the HOMO energy of the emitter and the LUMO energy ofthe first host is represented by ΔE1 and wherein 0.05 eV≤ΔE1−E_(ET)≤0.60eV.

FIG. 9 shows photoluminescence of Emitter 2 in poly (methylmethacrylate) at room temperature demonstrating the intrinsic emissionspectrum of Emitter 2. The 1931 CIE coordinates of this spectrum are(0.146,0.149).

There are a number of requirements for the e-host that increase theperformance of blue devices. The two foremost requirements for havingthe e-host to increase the lifetime of a device are: (1) the addition ofe-host does not form an exciplex or charge transfer (CT) state with theemitter; and (2) that the charges are balanced with an exciton profilenot pinned at an interface. Exiplex is an electronic state formedbetween two molecules, one a donor and the other an acceptor, which cansubsequently dissociate in a deactivation process. The requirement thatthe addition of the e-host does not form an exiplex or CT state as thelowest energy state in the device will maintain the blue color of thephosphorescent emitter. The CT state exists between the e-host and theother components when a hole resides on an emitter or a host moleculeand an electron resides on the e-host. A rough estimate of the CT stateenergy is the absolute value of the energy difference between the HOMOlevel of the emitter and the LUMO level of the e-host, ΔE1. Since the CTstate is composed of an electron and a hole that are fairly wellseparated spatially, the energy difference between the S₁ singlet andthe T₁ triplet state of the CT will be small and ΔE1 is a goodapproximation of the T₁ triplet state of the CT state. Having any CTstate (if formed) that is higher in energy than the T₁ triplet of theemitter is OK for device operation. If the CT state is higher in energythan the emitter's T₁, there are two important aspects for the device.First, the emission spectrum of the device will be that of the emitterand not the CT state. Second, there will be a minimal loss in emitter'sphotoluminescence quantum yield (PLQY) in the host system. Conversely,if the CT state is the lowest energy state in the emission system, theT₁ triplet of the emitter will be quenched into the CT state and the CTstate spectrum will dominate the device's emission spectrum.

For example, Table 3 contains the device structures and data for twodifferent single-component e-hosts for blue phosphorescence emitter(Emitter 2). The terms “device structures” here refers to the materialmake up of the layers in the device. In the results, we can see that alower energy CT state is formed when using Compound 1 (Cmp 1) as thehost material. This is readily observed by the change in the peakwavelength from 461 nm of Device 2 to the peak of 502 nm in Device 1.This can be seen in the emission spectrum of Device 1 and Device 2provided in FIG. 15. Further, the FWHM of Device 1 increases to 83 nmconsistent with a Gauassian emission spectrum that is typicallyexhibited when an exiplex is formed. With Compound 2 (Cmp 2) as thehost, the spectral emission of the blue device is very similar to thatof Emitter 2 drop cast in poly (methyl methacrylate) (PMMA), indicatingthat no CT state is formed with Compound 2 as the host. The emissionspectrum of Emitter 2 in drop cast PMMA at room temperature is shown inFIG. 9, which shows the emission spectrum of Emitter 2. The 1931 CIEcoordinates of this spectrum are (0.146,0.149) and the peak emissionwavelength is 452 nm.

TABLE 3 Device structures and data. This table is split into two parts.Device structure EML HIL HTL EBL Host Emitter BL ETL EIL 1931 CIE [100Å] [250 Å] [50 Å] [300 Å] [10%] [50 Å] [300 Å] [10 Å] x y Device 1 Cmp 5Cmp 6 Cmp 4 Cmp 1 Emitter 2 Cmp 2 Cmp 7: Cmp 8 35% Cmp 7 0.246 0.507Device 2 Cmp 5 Cmp 6 Cmp 4 Cmp 2 Emitter 2 Cmp 2 Cmp 7: Cmp 8 35% Cmp 70.155 0.282 at 10 mA/cm² λ max FWHM Voltage LE EQE PE [nm] [nm] [V][cd/A] [%] [lm/W] Device 1 502 83 3.6 11 3.7 9 Device 2 461 64 3.5 7 3.74.1 HIL = hole injection layer; HTL = hole transport layer; EBL =electron blocking layer; EML = emissive layer; BL = hole blocking layer;ETL = electron transport layer; EIL = electron injection layer; thedevices also had a 1000 Å Al cathode. All doping percenages are involume percent.

The experimentally realized CT state formed between Cmp 1 and Emitter 2can be verified by comparing ΔE to the T₁ triplet energy of Emitter 2.The HOMO level of Emitter 2, as determined by CV, is −5.37 and the LUMOlevel of Compound 1, as determined by CV, is −2.71. For the combinationof Compound 1 and Emitter 2, ΔE is 2.66 eV. For Emitter 2, the 77Kemission peak is at 449 nm which corresponds to a triplet energy of 2.76eV. Thus, we see that the CT state with energy ΔE is lower in energythan the T₁ triplet of Emitter 2. In turn, the device emission isdominated by the CT state, leading to non-blue emission and low externalquantum efficiency (EQE).

Compound 2 is the converse example. The LUMO level of Compound 2 is−2.47 eV as determined by CV. The ΔE for Emitter 2 and Compound 2 is2.90 eV which is greater than the 2.76 eV triplet energy of Emitter 2.This leads to the T₁ triplet energy of Emitter 2 being the lowest energystate in the device, as observed by the emission spectrum of the devicematching that of Emitter 2 in PMMA.

In addition to the avoidance of CT state formation, requirement (1), theuse of an electron transporting material in a deep blue phosphorescentdevice requires careful consideration of charge balance, requirement(2). A properly charge balanced device can greatly increase theefficiency and LT of the blue phosphorescent device and spreading theexciton profile over the thickness of the emissive layer can increaselifetime of the device.

In order to evaluate whether a given emissive layer composition spreadsthe exciton profile over the thickness of the emissive layer requiresthe ability to probe the location of the exciton population spatially.Inventors used a 20 Å thick sensing layer to probe the location of theexciton population in the emissive layer. FIG. 10 is a schematicdepiction of a red probe device 300 used with all of the layers otherthan the emissive layer (EML) 335 specified. The red probe device 300 iscomprised of an ITO (750 Å thick) anode layer 315; Compound 5 (100 Åthick) as a hole injection layer (HIL) 320; Compound 6 (250 Å thick) asa hole transport layer (HTL) 325; Compound 4 (50 Å thick) as an electronblocking layer (EBL) 330; EML 335; Compound 2 (50 Å thick) as a holeblocking layer (HBL) 340; Compound 7 and Compound 8 (300 Å thick; 65vol. %:35 vol. %) as a electron transport layer (ETL) 345; Compound 7(10 Å thick) as an electron injection layer (EIL) 350; and Al (1000 Åthick) as a cathode 360. The dashed lines 0A, 150A, and 300A identifythe locations, noted as the distance from the EBL/EML interface 332reported in angstroms, where 20 Å thick neat layers of Compound 9, a redemitter as red sensing layers, were deposited within the emissive layer335. Excitons on the blue phosphorescent molecules near the red sensinglayer will be quenched to become excitons on the red phosphorescentemitter; while excitons far away from the red sensing layer will not bequenched. Thus, devices with the red sensing layer will have acombination of red and blue emission. The more red emission in thespectrum of the device for a fixed amount of red dopant, the more blueexciton are within a transfer radius of the sensing layer. This means,that the more red emission in the spectrum, the more blue excitonsreside at that spatial location within the device. We assume that thequenching efficiency is independent of the number of blue excitons andthat the red emitter molecules do not perturb charge balance as thelayer is discontinuous (due to its 20 Å thickness).

FIG. 11A shows electroluminescent spectrum from the example red probedevice 300 with the probe layer of 20 Å of Compound 9 at a distance of0,150, and 300 Å from the EBL of Compound 4. FIG. 11B shows red to blueintensity ratio (R/B) as a function of the position of the sensinglayer. The higher the R/B value the larger the exciton population atthat spatial location. The measurement occurred at 10 mA/cm².

FIG. 12 is a plot of the R/B ratio of the device 300 at drivingdensities of 1, 10, and 100 mA/cm2.

FIGS. 13A-13C are plots of R/B ratio as a function of driving currentdensity for Device 2 a, Device 2 b, Device 2 c, and Device 2 d,respectively.

Using the red probe experiment and through varying the composition ofthe emissive layer we can demonstrate certain compositions that resultin either good exciton profiles and/or good charge stability. In doingso we will use the device structure of FIG. 10 where the composition ofthe emissive layer is varied.

Referring to FIGS. 11A and 11B, an example of understanding how the redsensing devices work will be described. FIG. 11A shows a plot of thenormalized emission spectrum of a red probe device with a 20 Å layer ofCompound 9 doped at various distances from the HTL-EML interface 332.The plot is normalized at the location of the peak emission of the blueemitter for clarity. The lines labeled as “0” “150” and “300” correspondto the three red sensing devices each having the red sensing layer ofCompound 9 at locations 0A, 150A, and 300A, shown in FIG. 10,respectively. It is readily apparent that there are different amounts ofred emission when the probe is at different spatial locations. To easilycompare across devices with different locations of the red sensinglayer, we can summarize the spectrum into a single number, the R/Bratio. The R/B ratio is the EL intensity at the peak wavelength of thered emitter divided by the EL intensity at the peak wavelength of theblue emitter. This represents the ratio of red to blue emission. Forprobe locations which have a high R/B ratio, this indicates that thereare a large number of blue excitons at this spatial location. If the R/Bratio is low, then the blue light is coming from blue excitons which arenot quenched by the red sensing layer and there are few blue excitons atthis spatial location. FIG. 11B is a plot of the R/B ratio for thedevices in FIG. 11A. The R/B ratio demonstrates that blue excitonsreside at the HTL-EML interface 332 and also the middle of the EML butnot at the ETL side of the EML.

In addition to having a good exciton profile, blue phosphorescentdevices should be stable to different charging current densities(electric field strengths). We can monitor the charge stability of adevice by monitoring the R/B ratio as a function of current density ofthe device. FIG. 12 is the R/B ratio of the same three devices of FIGS.11A and 11B measured at current densities 1, 10, and 100 mA/cm². The R/Bratio is normalized for each current density to allow for comparisonbetween different current densities of operation. In FIG. 12 the excitonprofile is strongly dependent on the current density. This is not idealfor creating stable devices. Instead, it would be better if the excitonprofile is nearly constant and centered in the middle of the device.

As an example to how to design a stable blue phosphorescent devices, wecan use Emitter 2. Emitter 2 is a blue phosphorescent emitter with apeak wavelength of emission at 460 nm in a device or 452 nm in PMMA anda PLQY of 70% in drop cast PMMA. Using the device structure shown inFIG. 10, we varied the host compounds which compose the emissive layerkeeping the amount of Emitter 2 fixed at 10% by volume. The deviceresults are provided in Table 4 below. In addition to the device resultsin Table 4, we performed red phosphorescent probe layer devices. Theresults of the R/B ratio as a function of current density are providedin FIGS. 13A-13D. FIGS. 13A, 13B, 13C, and 13D are the R/B ratio plotsfor the experimental devices 2 a, 2 b, 2 c, and 2 d, respectively, whoseEML compositions are provided in Table 4. Below we discuss the resultsof contained in these two figures and their implications for makingstable blue phosphorescent OLEDs.

TABLE 4 Device data table. The EML composition is noted. All other layerinformation is specified in FIG. 10. The lifetime is calculated assumingan acceleration factor of 1.8 at 1K 1931 CIE at 10 mA/cm² nits EMLcomposition λ max FWHM Voltage LE EQE PE calc* [280-300 Å] x y [nm] [nm][V] [cd/A] [%] [lm/W] 80% [h] Device Cmp 2: Emitter 2 0.156 0.236 460 533.41 4.5 2.7 4.1 15 2a 10% 280 Å Device Cmp 3: Emitter 2 0.153 0.218 46051 4.78 14.5 9.1 9.5 38 2b 10% 280 Å Device Cmp 3:Cmp 2: Emitter 2 0.1510.212 460 50 4.14 11.1 7.1 8.4 60 2c 40:10% 300 Å Device Cmp 3:Cmp 2:Cmp4: 0.155 0.244 460 55 4.04 17.0 9.9 13.2 57 2d Emitter 2 40:25:10% 300 Å

Devices which feature host compounds Cmp 2 and Cmp 3 are single hostcomponent devices, where Cmp 2 is an e-host and Cmp 3 is consider ah-host. The device with Cmp 2 does not show any evidence of exiplexemission with Emitter 2 showing that the first requirement for having astable blue phosphorescent device is satisfied. There are several itemsto note. First, the efficiency of this device is quite low. Second, thevoltage at 10 mA/cm2 is very low which is a positive. Third, the R/Bratio in FIG. 13A indicates that the excitons are all piled up at theEBL-EML interface 332. This conclusion is verified by making the samedevice without the EBL. We observe that the EQE at 10 mA/cm2 decreasesto 0.8% and the EL spectrum has some emission from the HTL layer. Thesetwo phenomena indicate significant quenching of Emitter 2 by the HTL.

In contrast to the single-component e-host device, the single-componenth-host has significantly higher EQE. However, this device has a highoperating voltage. Additionally, as seen in FIG. 13B the exciton profileat low current density is good but the profile is not stable to varyingthe current density.

This leads to the use of a device with energy levels equivalent to FIG.4. This device is composed of both Cmp3 and Cmp2. Using the bothelectron and hole conducting hosts gives a device with an EQE at 10mA/cm² of intermediate value between the two single component devices.However, the lifetime at 1,000 nits is greater than either of the singlecomponent devices. We observe in FIG. 13C that the exciton profile is atthe EBL-EML interface 332 which is not ideal and might explain why theEQE is lower than the single hole transporting device. This likely canbe shifted to the middle of the EML by lowering the electron conductinghost volume fraction. Never the less, the lifetime of the device issignificantly increased over that of the single-component devices.

To combat the good electron transport of the device with Cmp 3: Cmp2 40%we can add an additional h-host. The energetics of the host componentsare depicted in FIG. 7. This additional h-host should have a HOMO levelthat is as shallow as possible without forming an exiplex with theelectron conducting host or the emitter. This requires that the energydifference between the HOMO level of the second host (per FIG. 7) andthe LUMO of the electron conducting first host be greater than thetriplet energy of emitter 1 (per FIG. 7). The addition of this extrahost will add hole transport and move the exciton profile away from theEBL-EML interface 332. We also expect that the increase in holeconductivity will result in a lower voltage of operation. This is whatis observed with the fourth device in Table 2. The addition of Cmp 4 tothe emissive layer decreases voltage and increases EQE. In FIG. 13D, wesee that the exciton profile is moved to the center of the EML. Further,we observe that this exciton profile is stable to current density withthe profile hardly changing with driving current density. Finally, wenote that this device has the best combination of EQE, operatingvoltage, and lifetime. The addition of Cmp 4 did not significantlychange the stability of the device LT80 at 1,000 nits.

The overall conclusions from the red probed devices plus the deviceresults in Table 4 demonstrate managing the composition of the EML cangreatly improve device performance. However, the ideal composition canvary by emitter. For example, in Table 5 provided below we show thedevice performance of Emitter 3 for various EML compositions. The EMLcomposition of each device is noted in the table with the remaininglayers per FIG. 10. In this case, the device performance can be improvedover the single host case by using devices with energy level alignmentssimilar to FIGS. 4, 6B, and 13 which are demonstrate with devices 3 b, 3c, and 3 d respectively.

TABLE 5 Device data table. The EML composition is noted. All other layerinformation is specified in FIG. 10. at 1K at 10 mA/cm² nits EMLcomposition 1931 CIE λ max FWHM Voltage LE EQE PE calc* [300 Å] x y [nm][nm] [V] [cd/A] [%] [lm/W] 80% [h] Device 3a Cmp 10: Emitter 3 15% 0.1330.188 467 29 5.64 12.0 8.9 6.7 8 Device 3b Cmp 10:Cmp 2: Emitter 3 0.1320.191 467 33 4.03 9.3 6.8 7.3 19 40:10% Device 3c Cmp 10:Cmp 4: Emitter3 0.129 0.180 468 27 4.07 12.6 9.7 9.7 13 40:10% Device 3d Cmp 10:Cmp2:Cmp 4: 0.130 0.195 468 33 3.94 19.0 13.8 15.1 58 Emitter 3 40:25:10%

Table 5 highlights the following important information. First, use ofCompound 2 in the emissive layer at 40% doping lowers the EQE at 10mA/cm2 but increase the lifetime and lowers the operating voltagesimilar to Emitter 2. However, for Emitter 3, the addition of Compound 4to the emissive layer adds hole transport to the emissive layer whichincreases EQE, increases lifetime, and decreases operating voltagerelative to the single host device. Similar to Emitter 2, Emitter 3experiences the best EQE, lifetime, and operating voltage when usingCompound 10, Compound 2, and Compound 4 in the emissive layer.

The OLED disclosed herein can be incorporated into one or more of aconsumer product, an electronic component module, and a lighting panel.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:EP01617493, EP01968131, EP2020694, EP2684932, US20050139810,US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455,WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804,US20150123047, and US2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but are not limited to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butare not limited to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene; the group consistingof aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Each Ar may beunsubstituted or may be substituted by a substituent selected from thegroup consisting of deuterium, halide, alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are notlimited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, 0, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fe⁺/Fe couple lessthan about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used inan OLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334,EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701,EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765,JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473,TW201139402, U.S. Pat. No. 06,517,957, US20020158242, US20030162053,US20050123751, US20060182993, US20060240279, US20070145888,US20070181874, US20070278938, US20080014464, US20080091025,US20080106190, US20080124572, US20080145707, US20080220265,US20080233434, US20080303417, US2008107919, US20090115320,US20090167161, US2009066235, US2011007385, US20110163302, US2011240968,US2011278551, US2012205642, US2013241401, US20140117329, US2014183517,U.S. Pat. No. 5,061,569, U.S. Pat. No. 5,639,914, WO05075451,WO07125714, WO08023550, WO08023759, WO2009145016, WO2010061824,WO2011075644, WO2012177006, WO2013018530, WO2013039073, WO2013087142,WO2013118812, WO2013120577, WO2013157367, WO2013175747, WO2014002873,WO2014015935, WO2014015937, WO2014030872, WO2014030921, WO2014034791,WO2014104514, WO2014157018,

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and/or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and/or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Additional Hosts:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingdopant material, and may contain one or more additional host materialsusing the metal complex as a dopant material. Examples of the hostmaterial are not particularly limited, and any metal complexes ororganic compounds may be used as long as the triplet energy of the hostis larger than that of the dopant. Any host material may be used withany dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of other organic compounds used as additional host are selectedfrom the group consisting of aromatic hydrocarbon cyclic compounds suchas benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene,phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene;group consisting aromatic heterocyclic compounds such asdibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene,benzofuran, benzothiophene, benzoselenophene, carbazole,indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole,triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole,thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine,oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole,indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline,isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine,phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine,phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. k is an integer from 0 to 20 or 1 to 20. X¹⁰¹ toX¹⁰⁸ are independently selected from C (including CH) or N. Z¹⁰¹ andZ¹⁰² are independently selected from NR¹⁰¹, O, or S.

Non-limiting examples of the additional host materials that may be usedin an OLED in combination with the host compound disclosed herein areexemplified below together with references that disclose thosematerials: EP2034538, EP2034538A, EP2757608, JP2007254297,KR20100079458, KR20120088644, KR20120129733, KR20130115564, TW201329200,US20030175553, US20050238919, US20060280965, US20090017330,US20090030202, US20090167162, US20090302743, US20090309488,US20100012931, US20100084966, US20100187984, US2010187984, US2012075273,US2012126221, US2013009543, US2013105787, US2013175519, US2014001446,US20140183503, US20140225088, US2014034914, U.S. Pat. No. 7,154,114,WO2001039234, WO2004093207, WO2005014551, WO2005089025, WO2006072002,WO2006114966, WO2007063754, WO2008056746, WO2009003898, WO2009021126,WO2009063833, WO2009066778, WO2009066779, WO2009086028, WO2010056066,WO2010107244, WO2011081423, WO2011081431, WO2011086863, WO2012128298,WO2012133644, WO2012133649, WO2013024872, WO2013035275, WO2013081315,WO2013191404, WO2014142472, US20170263869, US20160163995, U.S. Pat. No.9,466,803.

Emitter:

An emitter example is not particularly limited, and any compound may beused as long as the compound is typically used as an emitter material.Examples of suitable emitter materials include, but are not limited to,compounds which can produce emissions via phosphorescence, fluorescence,thermally activated delayed fluorescence, i.e., TADF (also referred toas E-type delayed fluorescence; see, e.g., U.S. application Ser. No.15/700,352, which is hereby incorporated by reference in its entirety),triplet-triplet annihilation, or combinations of these processes.

Non-limiting examples of the emitter materials that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526,EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907,EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652,KR20120032054, KR20130043460, TW201332980, US06699599, US06916554,US20010019782, US20020034656, US20030068526, US20030072964,US20030138657, US20050123788, US20050244673, US2005123791, US2005260449,US20060008670, US20060065890, US20060127696, US20060134459,US20060134462, US20060202194, US20060251923, US20070034863,US20070087321, US20070103060, US20070111026, US20070190359,US20070231600, US2007034863, US2007104979, US2007104980, US2007138437,US2007224450, US2007278936, US20080020237, US20080233410, US20080261076,US20080297033, US200805851, US2008161567, US2008210930, US20090039776,US20090108737, US20090115322, US20090179555, US2009085476, US2009104472,US20100090591, US20100148663, US20100244004, US20100295032,US2010102716, US2010105902, US2010244004, US2010270916, US20110057559,US20110108822, US20110204333, US2011215710, US2011227049, US2011285275,US2012292601, US20130146848, US2013033172, US2013165653, US2013181190,US2013334521, US20140246656, US2014103305, U.S. Pat. No. 6,303,238, U.S.Pat. No. 6,413,656, U.S. Pat. No. 6,653,654, U.S. Pat. No. 6,670,645,U.S. Pat. No. 6,687,266, U.S. Pat. No. 6,835,469, U.S. Pat. No.6,921,915, U.S. Pat. No. 7,279,704, U.S. Pat. No. 7,332,232, U.S. Pat.No. 7,378,162, U.S. Pat. No. 7,534,505, U.S. Pat. No. 7,675,228, U.S.Pat. No. 7,728,137, U.S. Pat. No. 7,740,957, U.S. Pat. No. 7,759,489,U.S. Pat. No. 7,951,947, U.S. Pat. No. 8,067,099, U.S. Pat. No.8,592,586, U.S. Pat. No. 8,871,361, WO06081973, WO06121811, WO07018067,WO07108362, WO07115970, WO07115981, WO08035571, WO2002015645,WO2003040257, WO2005019373, WO2006056418, WO2008054584, WO2008078800,WO2008096609, WO2008101842, WO2009000673, WO2009050281, WO2009100991,WO2010028151, WO2010054731, WO2010086089, WO2010118029, WO2011044988,WO2011051404, WO2011107491, WO2012020327, WO2012163471, WO2013094620,WO2013107487, WO2013174471, WO2014007565, WO2014008982, WO2014023377,WO2014024131, WO2014031977, WO2014038456, WO2014112450,

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar³ has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

In another aspect, the metal complexes used in ETL include, but are notlimited to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms 0, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

Non-limiting examples of the ETL materials that may be used in an OLEDin combination with materials disclosed herein are exemplified belowtogether with references that disclose those materials: CN103508940,EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918,JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977,US2007018155, US20090101870, US20090115316, US20090140637,US20090179554, US2009218940, US2010108990, US2011156017, US2011210320,US2012193612, US2012214993, US2014014925, US2014014927, US20140284580,U.S. Pat. No. 6,656,612, U.S. Pat. No. 8,415,031, WO2003060956,WO2007111263, WO2009148269, WO2010067894, WO2010072300, WO2011074770,WO2011105373, WO2013079217, WO2013145667, WO2013180376, WO2014104499,WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated,and fully deuterated versions thereof. Similarly, classes ofsubstituents such as, without limitation, alkyl, aryl, cycloalkyl,heteroaryl, etc. also encompass undeuterated, partially deuterated, andfully deuterated versions thereof.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. An organic light emitting device (OLED), comprising: an anode; acathode; and an organic emissive layer disposed between the anode andthe cathode, the organic emissive layer comprising: a first host havinga highest occupied molecular orbital (HOMO) energy, a lowest unoccupiedmolecular orbital (LUMO) energy, and a T₁ triplet energy; and an emitterhaving a highest occupied molecular orbital (HOMO) energy, a lowestunoccupied molecular orbital (LUMO) energy, and a T₁ triplet energy;wherein the emitter is selected from the group consisting of aphosphorescent metal complex, and a delayed fluorescent emitter; whereinE_(HIT), the T₁ triplet energy of the first host, is higher than E_(ET),the T₁ triplet energy of the emitter; wherein E_(ET) is at least 2.50eV; wherein the LUMO energy of the first host is higher than the HOMOenergy of the emitter; wherein the absolute value of the differencebetween the HOMO energy of the emitter and the LUMO energy of the firsthost is ΔE1; wherein a≤ΔE1-E_(ET)≤b; and wherein a≥0.05 eV, and b≥0.60eV. 2.-14. (canceled)
 15. The OLED of claim 1, wherein the first host isan electron transporting host.
 16. The OLED of claim 1, wherein theabsolute value of the difference between the highest HOMO energy and thelowest LUMO energy among all components in the emissive layer is largerthan E_(ET) by at least a.
 17. The OLED of claim 1, wherein the OLEDfurther comprises a second host; wherein E_(H2T), the T₁ triplet energyof the second host, is higher than E_(ET).
 18. The OLED of claim 17,wherein the HOMO energy of the second host is lower than the HOMO energyof the first host, the LUMO energy of the second host is higher than theLUMO energy of the first host.
 19. The OLED of claim 17, wherein theHOMO energy of the second host is higher than the HOMO energy of thefirst host, the LUMO energy of the second host is higher than the LUMOenergy of the first host.
 20. The OLED of claim 17, wherein thedifference of HOMO energy between the first and the second host is from0.1 to 0.6 eV.
 21. The OLED of claim 17, wherein the difference of HOMOenergy between the emitter and the second host is from 0.05 to 0.8 eV.22. The OLED of claim 17, wherein the second host is a hole transportinghost.
 23. The OLED of claim 1, wherein the device has an operationvoltage less than 6.0 V at 10 mA/cm². 24.-25. (canceled)
 26. The OLED ofclaim 1, wherein the first host comprises at least one chemical groupselected from the group consisting of pyridine, pyrimidine, pyrazine,triazine, imidazole, aza-tripheny lene, aza-carbazole,aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. 27.(canceled)
 28. The OLED of claim 1, wherein the emitter has the formulaof M(L¹)_(x)(L²)_(y)(L³)_(z); wherein L¹, L² and L³ can be the same ordifferent; wherein x is 1, 2, or 3; wherein y is 0, 1, or 2; wherein zis 0, 1, or 2; wherein x+y+z is the oxidation state of the metal M;wherein L¹, L² and L³ are each independently selected from the groupconsisting of:

wherein each X¹ to X¹⁷ are independently selected from the groupconsisting of carbon and nitrogen; wherein X is selected from the groupconsisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, andGeR′R″; wherein R′ and R″ are optionally fused or joined to form a ring;wherein each R_(a), R_(b), R_(c), and R_(d) may represent from monosubstitution to the possible maximum number of substitution, or nosubstitution; wherein R′, R″, R_(a), R_(b), R_(c), and R_(d) are eachindependently selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl,alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof; and wherein any two R_(a), R_(b),R_(c), and R_(d) are optionally fused or joined to form a ring or form amultidentate ligand.
 29. (canceled)
 30. The OLED of claim 28, whereinthe compound has the formula selected from the group consisting ofIr(L¹)(L²)(L³), Ir(L¹)₂(L²), and Ir(L¹)₃; wherein L¹, L² and L³ aredifferent and each independently selected from the group consisting of:


31. The OLED of claim 28, wherein the compound has the formula ofPt(L¹)₂ or Pt(L¹)(L²).
 32. (canceled)
 33. The OLED of claim 28, whereinthe compound has the formula of M(L¹)₂ or M(L¹)(L²); wherein M is Ir,Rh, Re, Ru, or Os, L¹ and L² are each a different tridentate ligand. 34.The OLED of claim 28, wherein L′,is selected from the group consistingof:


35. A consumer product comprising an OLED according to claim
 1. 36. Theconsumer product of claim 35, wherein the consumer product is one of aflat panel display, a curved display, a computer monitor, a medicalmonitor, a television, a billboard, a light for interior or exteriorillumination and/or signaling, a heads-up display, a fully or partiallytransparent display, a flexible display, a rollable display, a foldabledisplay, a stretchable display, a laser printer, a telephone, a mobilephone, a tablet, a phablet, a personal digital assistant (PDA), awearable device, a laptop computer, a digital camera, a camcorder, aviewfinder, a micro-display, a 3-D display, a virtual reality oraugmented reality display, a vehicle, a video wall comprising multipledisplays tiled together, a theater or a stadium screen, and a sign. 37.An organic light emitting device (OLED), comprising: an anode; acathode; and an organic emissive layer disposed between the anode andthe cathode comprising: a first host having a highest occupied molecularorbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO)energy, and a T₁ triplet energy; a second host having a highest occupiedmolecular orbital (HOMO) energy, a lowest unoccupied molecular orbital(LUMO) energy, and a T₁ triplet energy; and an emitter having a highestoccupied molecular orbital (HOMO) energy, a lowest unoccupied molecularorbital (LUMO) energy, and a T₁ triplet energy; wherein the emitter isselected from the group consisting of a phosphorescent metal complex,and a delayed fluorescent emitter; wherein EmT, the T₁ triplet energy ofthe first host, is higher than E_(ET), the T₁ triplet energy of theemitter; wherein E_(ET) is at least 2.50 eV; wherein the HOMO energy ofthe first host is higher than the HOMO energy of the second host;wherein the absolute value of the difference between the HOMO energy ofthe emitter and the HOMO energy of the first host is ΔE2; wherein ΔE2≤d;wherein d is 1.2 eV; wherein the absolute value of the differencebetween the LUMO energy of the emitter and the HOMO energy of the firsthost is ΔE3; wherein a≤ΔE3-E_(ET)≤b; and wherein a≥0.05 eV and b is≥0.60 eV. 38.-41. (canceled)
 42. An organic light emitting device(OLED), comprising: an anode; a cathode; and an organic emissive layerdisposed between the anode and the cathode, the organic emissive layercomprising: a first host having a highest occupied molecular orbital(HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, anda T₁ triplet energy; a second host having a highest occupied molecularorbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO)energy, and a T₁ triplet energy; a third host having a highest occupiedmolecular orbital (HOMO) energy, a lowest unoccupied molecular orbital(LUMO) energy, and a T₁ triplet energy; and an emitter having a highestoccupied molecular orbital (HOMO) energy, a lowest unoccupied molecularorbital (LUMO) energy, and a T₁ triplet energy; wherein the emitter is aphosphorescent metal complex having E_(ET), T₁ triplet energy, of atleast 2.50 eV; wherein the LUMO energy of the first host is higher thanthe HOMO energy of the emitter; wherein the absolute value of thedifference between the HOMO energy of the emitter and the LUMO energy ofthe first host is ΔE1; wherein the HOMO energy of the second host islower than the HOMO energy of the emitter; wherein the absolute value ofthe difference between the HOMO energy of the emitter and the HOMOenergy of the second host is ΔE4; wherein a≤ΔE1-E_(ET)≤b, whereina≥0.005 eV and b≥0.60 eV; wherein ΔE4≤d, wherein d is 1.2 eV; andwherein the HOMO energy of the third host is lower than the HOMO energyof the second host 43.-51. (canceled)